in spare moments; between tasks; whenever there's a break
Used adverbially, often with に, to describe doing something during the gaps in one's schedule or while waiting. Implies using small pockets of free time productively.
I do stretches in the spare moments between work tasks.
I try to memorize vocabulary whenever I have a spare moment.
Reduplication of 合間 (あいま, 'interval, break'), emphasizing the idea of 'in every little break' or 'whenever there is a spare moment'.